1. Field of the Invention
This invention relates to antenna systems; and more particularly to an integrated antenna system adapted for multi-input multi-output (MIMO) operation.
2. Description of the Related Art
In view of continuous improvements within the field of wireless communication technology, the trend in the tele-communication industry is to move to 4th generation, or 4G communication systems, for increased data rate requirements. The improved data rates achieved by 4G communication systems require multiple antennas on one or both ends of the communication link. This Multiple Input Multiple Output (MIMO) protocol and modulation scheme commonly requires multiple antennas operating in the same frequency band to be integrated into portable as well as stationary communication devices. The multiple antennas situated in the portable electronic devices, such as laptop computers, mobile phones, and personal digital assistants (PDAs) must work in unison to receive and transmit multiple data streams. These MIMO antennas are required to maintain high isolation and low pattern correlation for optimum link quality and to achieve the desired high data rates compared to 2G and 3G communication protocols. For portable electronic devices in particular, reduced size and reduced antenna inter-element spacing is required to integrate the multiple antennas into small and lightweight form factors.
Current antenna system design and integration techniques consist of designing a baseline antenna adapted to cover the frequency bands of interest, and then placing duplicates of this baseline design at various locations within the communication device to satisfy the MIMO antenna requirement. Care must be taken to insure that isolation, as well as low pattern correlation is maintained between the individual antennas. Low pattern correlation can be achieved by maintaining specific distances between antenna elements or by varying the polarization state of one antenna in the MIMO system compared to the other antennas in the system. The antenna design process is complicated by the multiple frequency bands that many MIMO antenna systems are required to cover.
The conventional multiple-band antenna such as a planar inverted-F antenna (PIFA) is generated from a two dimensional design. The PIFA can be provided from a printed circuit board (PCB) which has copper foil to be processed into a two dimensional shape, or can be provided as a three dimensional design from metal sheet forming processes. The two dimensional shape lends itself to photo-etching techniques on PCBs and aids in integration into portable electronic devices due to reduced volume of the two dimensional design.
The requirements for high isolation and low correlation between pairs of antennas also apply to 3G communication requirements such as receive diversity schemes for improved signal reception in multi-path environments. As in 4G communication systems, antenna spacing and orientation of one antenna in relation to the other antennas are important in 3G antenna systems to provide for improved data rates and connectivity.
Additionally, Wifi and wireless local area network (WLAN) communication devices also require multiple antenna systems where stringent spacing and orientation requirements are needed to provide for improved signal transmission and reception. Two antenna systems for Wifi and WLAN have been the norm for several years due to the benefits of spatial diversity between pairs of antennas in defeating the effects of deep signal fades due to multi-path reception.
With the requirement of maintaining a specific spacing between antenna elements in a MIMO antenna system for maintaining high isolation and low pattern correlation, a solution for integrating multiple antennas into a portable electronic device as well as stationary devices is needed, wherein inter-element spacing between antenna elements can be maintained in a production setting, such that automated or manual assembly techniques can be reliably implemented.